The present invention relates generally to brush seals for sealing between a turbine rotor and a stationary component about the rotor and particularly relates to a method of attachment for a raised platform sealing surface provided on the rotor for engagement by the tips of the bristles of the brush seal whereby rotor dynamic and thermal constraints on the use of brush seals in diaphragm packing areas of the turbine are overcome.
As explained in detail in U.S. Pat. No. 6,168,377B1 of common assignee, it is desirable to employ brush seals for sealing between a turbine rotor, and the stationary rotor casing since brush seals have demonstrably improved sealing characteristics as compared with labyrinth type seals typically used at those seal locations. However, rotor dynamic and thermal constraints inhibit use of brush seals for example in the diaphragm packing area of a steam turbine. Localized rotor heating due to the friction caused by the bristles of the brush seal rubbing on the rotor surface magnifies the effects of rotor vibrations through the first and second critical speeds resulting in unacceptable radial rotor movement. Impulse design steam turbines typically operate above the rotors first bending critical frequency and often near the second bending critical frequency. This sustained rubbing and heat generated thereby can cause thermal bowing of the rotor or exacerbate an existing bowed condition of the rotor. Accordingly, there is a need to minimize or eliminate the rotor dynamic and thermal constraints to the use of brush seals in turbine rotors to enable widespread use of brush seals in turbine seal locations previously constrained from such use.
In accordance with the preferred embodiment of the present invention, there is provided an insert for securement on the rotor affording a raised annular continuous sealing surface in contact with the brush seal bristle tips to dissipate frictional heat without affecting rotor vibrational characteristics. Particularly, the rotor is provided with a locking device for locking a plurality of platform sealing segments about the rotor to form and thus locate the annular sealing surface in a position raised radially from the surface of the rotor. In this manner, heat is dissipated outwardly of the rotor surface with minimal or no thermal effect on the rotor. The locking device preferably includes a pair of axially spaced rims each having a flange radially spaced from the rotor surface. The flanges extend axially toward one another and have a plurality of axially extending teeth spaced circumferentially one from the other defining slots therebetween.
A plurality of platform sealing segments are provided for securement to the locking device. Each platform segment has an arcuate sealing surface portion which, when the platform segments are secured to the locking device, form the continuous annular sealing surface about and rotor and engageable by the tips of the brush seal bristles. Each segment preferably includes a circumferentially extending securing element, preferably a pair of elements. Each element has a flange which extends axially away from the flange of the other element and is spaced radially inwardly from the segment body. The platform segment flanges have a plurality of circumferentially spaced teeth separated by slots.
To install the platform sealing segments, the teeth of the platform segments are aligned with the slots between the teeth of the locking device. When aligned, the segments are displaced radially inwardly to locate the teeth of the segments inwardly of the teeth of the locking device. It will be appreciated that when the segments are located in this manner, a continuous annular sealing surface is formed about the segments. To secure the segments to the locking device, the segments are rotated as a unit in a circumferential direction about the rotor axis to locate the platform sealing segment teeth radially inwardly of and in engagement with the overlying teeth of the locking device. Each segment is rotated to a positive tooth stop integral to the platform, the direction of assembly being counter to the direction of rotor rotation. By locking one segment to the locking device, for example by employing one or more grub screws or by staking or welding the segment in place, circumferential rotation of the annular sealing platform relative to the rotor is precluded. It will be appreciated that the contact between the brush seal and the platform is located radially outwardly of the adjacent rotor surfaces thus dissipating the frictional heat outwardly of the rotor surface. Additionally, the platform sealing segment surfaces and locking device can be used on single and opposed flow steam turbines during retrofit.
In a preferred embodiment according to the present invention, there is provided a turbine comprising a rotor and a non-rotatable component about the rotor, a brush seal carried by the non-rotatable component, an arcuate sealing platform interposed between the brush seal and the rotor and having an arcuate seal surface radially outwardly of an outer surface of the rotor, a locking device carried by the rotor, the locking device and the sealing platform having interengageable elements responsive to circumferential movement of the locking device and the platform relative to one another for locking the platform against radial outward movement relative to the rotor, the interchangeable elements including locking teeth carried by the locking device at axial spaced locations along the rotor and facing axially toward one another, the interchangeable elements including locking teeth carried by the platform at axially spaced locations therealong and facing in respective opposite axial directions away from one another, the teeth carried by the platform lying radially inwardly of the teeth of the locking device when the platform and locking device are locked to one another and the brush seal being engageable with the arcuate seal surface to seal between the rotor and the non-rotatable component.
In a further preferred embodiment according to the present invention, there is provided a steam turbine comprising a rotor having adjacent rotor stages each including a plurality of buckets and a diaphragm about the rotor straddled by the buckets, a brush seal carried by the diaphragm, an arcuate sealing platform interposed between the brush seal and the rotor, the platform having an arcuate seal surface raised radially outwardly of a rotor surface between the bucket stages, a locking device carried by the rotor for locking the platform against radial outward movement relative to the rotor, the locking device including a pair of axially spaced rims about the rotor and the platform includes a plurality of arcuate platform sealing segments having discrete seal surface portions forming the seal surface, the seal surface being continuous and annular about the rotor, a plurality of locking teeth carried by the rims facing axially toward one another and spaced radially outwardly of the rotor and between the bucket stages, a plurality of locking teeth carried by each of the platform sealing segments and extending in axially opposite directions away from one another, the teeth carried by the platform sealing segments lying radially inwardly of the teeth of the locking device when the platform and locking device are locked to one another, the brush seal being engageable with the arcuate seal surface to seal between the rotor and the diaphragm outwardly of the rotor surface enabling dissipation of frictionally generated heat by contact between the brush seal and the platform with minimal, if any, thermal effect on the rotor.
In a further preferred embodiment according to the present invention, there is provided in a steam turbine having a rotor and a non-rotatable component about the rotor carrying a brush seal for sealing between the rotor and the non-rotatable component, a method of installing a sealing platform on the rotor to afford a sealing surface for the brush seal comprising the steps of (a) providing a locking device at a predetermined axial position on the rotor including forming a first plurality of teeth at axially spaced locations along the rotor and extending in axial directions toward one another and at radial locations outwardly of adjacent surface portions of the rotor, the first teeth being spaced one from the other to form slots therebetween, b) providing platform segments having sealing surface portions at circumferential locations about the rotor substantially in radial registration with the locking device, including forming each segment with a plurality of second teeth at axially spaced locations therealong and extending in axial directions opposite to one another, the second teeth of each segment being spaced from one another to form slots therebetween and (c) securing the segments to the rotor by engaging the segments with the locking device including passing the second teeth of the platform segments through the slots between the first teeth, passing the first teeth of the locking device through the slots between the second teeth and rotating the platform segments and the locking device relative to one another to locate the second teeth between the first teeth and the rotor surface and enabling the sealing surface portions of the platform segments to form a continuous uninterrupted annular sealing surface about the rotor for engagement with the brush seal.